منابع مشابه
Spiral Galaxies Puzzles are NP-complete
We will show that the question of whether or not a given Spiral Galaxies puzzle has a solution is NP-complete. To do so, we construct Spiral Galaxies puzzles which correspond to arbitrary Boolean circuits. A circuit will be satisfied, (that is, have a set of inputs which give the desired outputs) if and only if the corresponding puzzle has a solution. Since Satisfiability is the canonical NP-co...
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Expanding supershells are perhaps the most prominent manifestation of the violent impact which massive stars have on the gaseous ISM. Commonly thought to be formed as a consequence of mechanical luminosity dumped into the ISM by OB associations, supershells can be viewed as a critical gauge of the energy source which ultimately supports interstellar turbulence. I will review the present underst...
متن کاملKinematically Lopsided Spiral Galaxies
Asymmetries in the distribution of light and neutral hydrogen are often observed in spiral galaxies. Here, attention is drawn to the presence of large-scale asymmetries in their kinematics. Two examples of kinematically lopsided galaxies are presented and discussed. The shape of the rotation curve –rising more steeply on one side of the galaxy than on the other– is the signature of the kinemati...
متن کاملAre Passive Spiral Galaxies Truly “Passive” and “Spiral”? : Near-Infrared Perspective
Passive spiral galaxies — unusual galaxies with spiral morphology without any sign of ongoing star formation — have recently been discovered to exist preferentially in cluster infalling regions (at about the virial radius, or at a local galaxy density of ∼ 1 Mpc). The discovery directly connects the passive spiral galaxies to the cluster galaxy evolution studies such as the Butcher-Oemler effec...
متن کاملAre Mirror Worlds Opaque?
Over the last few years, many close orbiting (∼ 0.05 A.U.) large mass planets (∼ M J) of nearby stars have been discovered. Their existence has been inferred from tiny Doppler shifts in the light from the star and in one case a transit has been observed. Because ordinary planets are not expected to be able to form this close to ordinary stars due to the high temperatures, it has been speculated...
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ژورنال
عنوان ژورنال: Nature
سال: 1990
ISSN: 0028-0836,1476-4687
DOI: 10.1038/346105a0